1. Field of the Invention
The present invention relates to a method for making a mask pattern, and more particularly to a method for making a mask pattern by correcting the size of a hole diameter of a mask for forming a contact hole.
2. Description of the Background Art
Making of a contact hole is indispensable in fabrication of LSI, and low precision of the hole diameter of a contact hole (hereinafter called contact hole diameter) leads to a contact failure previously control of the contact hole diameter has been attempted by correcting the mask pattern for forming a contact hole.
FIG. 24 is a flowchart showing a conventional technique of correcting the hole diameter of a mask (hereinafter called mask hole diameter) for forming a contact hole.
First, while making a mask pattern by using CAD, a check card is prepared. A check card is a collection of process flow for fabricating an LSI, specifying when to use which mask, when to make or remove which layer, etc.
Conventionally, by trial fabrication of LSI using a designed mask, the section of the LSI was observed by a microscope, and the actual contact hole diameter was measured. When the contact hole diameter was larger than a desired value, the mask hole diameter was designed smaller, and when the contact hole diameter was smaller than a desired value, the mask hole diameter was designed larger, and thus the mask pattern was corrected by such feedback.
For example, using a mask hole diameter designed to fabricate a contact hole diameter of 0.5 xcexcm, if the actually fabricated contact hole diameter is 0.4 xcexcm, the mask hole diameter is designed so as to fabricate a contact hole diameter of 0.6 xcexcm. Or, if the fabricated contact hole diameter is 0.6 xcexcm, the mask hole diameter is designed so as to fabricate a contact hole diameter of 0.4 xcexcm.
It is, however, not practical to execute this step for all contact holes. In the LSI, there are hundreds of thousands of contact holes on one chip.
In such circumstances, it is also attempted to loosen the design rule of the LSI. The contact hole diameter depends not only on the mask hole diameter, but also on the undulations of the region for forming the contact hole, and therefore when the undulations of the region are moderate, the precision of the contact hole diameter is enhanced. Accordingly, for example, if forming of lithographic pattern is possible at 0.5 xcexcm, then by designing the LSI by the 1 xcexcm rule, undulations in the region for forming the contact hole are set to moderate, and hence the precision of the contact hole diameter may be enhanced. It, however, requires a wide area for realizing the LSI, and the transmission characteristic of the element deteriorates.
A first aspect of the invention relates to a method of making a mask pattern, by correcting a mask pattern used for providing an actual pattern in a processing region of an object, comprising steps of (a) making the mask pattern, (b) judging undulations of the object, (c) predicting dimensions of the actual pattern depending on the degree of the undulations, and (d) correcting by giving a correction amount to the dimensions of the mask pattern, depending on the result of the step (c).
A second aspect of the invention relates to a method of making a mask pattern of the first aspect, wherein the actual pattern is provided by forming a resist on the object, and shaping the resist depending on the mask pattern, and the step (c) includes steps of (c-1) determining the film thickness increment or decrement of the resist in the processing region, on the basis of the film thickness of the resist when the object is flat, and (c-2) predicting, on the basis of the film thickness increment or decrement, that the direction of deviation of the dimensions of the actual pattern when the processing region is concave as compared with the actual pattern when the processing region is flat, and the direction of the dimensions of the actual pattern when the processing region is convex as compared with the actual pattern when the processing region is flat are reverse to each other, and that the dimensions of the actual pattern are deviated larger when the degree of undulations of the processing region is greater as compared with when the processing region is flat.
A third aspect of the invention relates to a method of making a mask pattern of the second aspect, wherein a surface shape of the object is recognized as a surface height, relative to a foundation region expanding at least in a first direction and a second direction reverse to the first direction, and the step (b) includes steps of (b-1) determining the surface height by simulation, (b-2) specifying the position of the processing region in the foundation region, (b-3) setting a first region expanding in the first direction from the processing region, and a second region expanding in the second direction from the processing region, (b-4) detecting whether a first state of the surface height tending to increase relative to the first direction or a second state tending to decrease relative to the first direction is present, in both the first and second regions, on the basis of the result of the step (b-1), and (b-5) judging undulations about the first and second directions in the processing region on the basis of the result of the step (b-4).
A fourth aspect of the invention relates to a method of making a mask pattern of the third aspect, wherein the step (b-4), respectively in the first and second regions, has steps of (b-4-1) determining a position for taking the maximum value of the surface height, (b-4-2) determining a position for taking the minimum value of the surface height, (b-4-3) determining a shape height by subtracting the surface height of the processing region from the maximum value, (b-4-4) determining a shape depth by subtracting the minimum value from the surface height of the processing region, (b-4-5) judging a presence of the first state when the shape height is greater than the shape depth, and (b-4-6) judging a presence of the second state when the shape height is smaller than the shape depth.
A fifth aspect of the invention relates to a method of making a mask pattern of the fourth aspect, wherein the step (b-4-5) comprises, when the shape height is greater than the shape depth, a step of (b-4-5-1) taking the shape height as a first value, the step (b-4-6) comprises, when the shape height is smaller than the shape depth, a step of (b-4-6-1) taking the value multiplying the shape depth by (xe2x88x921) as the first value, the step (c-1) has steps of (c-1-1) obtaining an altitude amount at an intermediate value of the first value of the first region and the first value of the second region, and (c-1-2) determining the film thickness increment or decrement on the basis of the altitude amount, and the absolute value of the film thickness increment or decrement is greater when the absolute value of the altitude amount is greater, and the sign of the altitude amount and the sign of the film thickness increment or decrement are different from each other, in the step (c-1-2).
A sixth aspect of the invention relates to a method of making a mask pattern of the fifth aspect, wherein the step (c-1-1) comprises a step of (c-1-1-1) obtaining an slope amount at an intermediate value of the value of dividing the first value in the first region by the second value in the first region, and the value of dividing the first value in the second region by the second value in the second region, and the film thickness increment or decrement is determined also on the basis of the slope amount in the step (c-1-2), and the absolute value of the film thickness increment or decrement is greater when the absolute value of the slope amount is greater.
A seventh aspect of the invention relates to a method of making a mask pattern of the fourth aspect, wherein the step (b-4-5) comprises, when the shape height is greater than the shape depth, steps of (b-4-5-1) taking the shape height as a first value, and (b-4-5-2) taking the distance along the first direction between the processing region and the position obtained in the step (b-4-1) as a second value, the step (b-4-6) comprises, when the shape height is smaller than the shape depth, steps of (b-4-6-1) taking the value multiplying the shape depth by (xe2x88x921) as the first value, and (b-4-6-2) taking the distance along the first direction between the processing region and the position determined in the step (b-4-2) as the second value, the step (c-1) has steps of (c-1-1) obtaining an altitude amount at either the first value in the first region or the first value in the second region, on the basis of the magnitude relation between a third value obtained by dividing the first value in the first region by the second value in the first region, and a fourth value obtained by dividing the first value in the second region by the second value in the second region, and (c-1-2) determining the film thickness increment or decrement on the basis of the altitude amount, and the absolute value of the film thickness increment or decrement is greater when the absolute value of the altitude amount is greater in the step (c-1-2), and the sign of the altitude amount and the sign of the film thickness increment or decrement are different from each other.
An eighth aspect of the invention relates to a method of making a mask pattern of the seventh aspect, wherein the step (c-1-1) comprises a step of (c-1-1-1) taking either the third value or the fourth value as the slope amount, on the basis of the magnitude relation of the third value and the fourth value, and the film thickness increment or decrement is determined also on the basis of the slope amount in the step (c-1-2), and the absolute value of the film thickness increment or decrement is greater when the absolute value of the slope amount is greater.
A ninth aspect of the invention relates to a method of making a mask pattern of the second aspect, wherein the step (c-2) includes a step of (c-2-1) determining a pattern increment or decrement deviated when compared with the actual pattern in the case that the dimension of the actual pattern is flat in the processing region, on the basis of the film thickness increment or decrement, and an index showing a characteristic to an irradiation ray for photosensitizing the resist.
A tenth aspect of the invention relates to a method of making a mask pattern of the third aspect, wherein the foundation range further expands in a third direction orthogonal to the first and second directions, and a fourth direction opposite to the third direction, a third region expanding from the processing region in the third direction, and a fourth region expanding from the processing region in the fourth region are further set in the step (b-3), presence or absence of the first state and the second state with respect to the third direction is further detected in the third and fourth regions in the step (b-4), undulations about the third and fourth directions in the processing region are further judged in the step (b-5), and the dimension of the actual pattern about the third and fourth directions is also predicted, together with the dimension of the actual patter about the first and second directions in the step (c-1).
An eleventh aspect of the invention relates to a method of making a mask pattern of the second aspect, wherein the surface shape of the object is understood as a surface height to a foundation region expanding in direction I and direction J orthogonal thereto, and the step (b) includes steps of (b-1) determining the surface height by simulation, (b-2) specifying the position of the processing region in the foundation range, (b-3) setting a first region expanding in a positive direction from the processing region, and a second region expanding in a negative direction from the processing region, with respect to the direction I and direction J, respectively, (b-4) detecting whether the surface height is in a first state in increasing tendency or in a second state in decreasing tendency, about the positive direction, in the first and second regions, with respect to the direction I and direction J, respectively, on the basis of the result of the step (b-1), and (b-5) judging undulations about the direction I and direction J of the processing region on the basis of the result of the step (b-4).
A twelfth aspect of the invention relates to a method of making a mask pattern of the eleventh aspect, wherein the step (b-4) has, respectively in the first and second regions, steps of (b-4-1) determining a position for taking the maximum value of the surface height, (b-4-2) determining a position for taking the minimum value of the surface height, (b-4-3) determining a shape height by subtracting the surface height of the processing region from the maximum value, (b-4-4) determining a shape depth by subtracting the minimum value from the surface height of the processing region, (b-4-5) judging the presence of the first state when the shape height is greater than the shape depth, and (b-4-6) judging the presence of the second state when the shape height is smaller than the shape depth.
A thirteenth aspect of the invention relates to a method of making a mask pattern of the twelfth aspect, wherein the step (b-4-5) comprises, when the shape height is greater than the shape depth, steps of (b-4-5-1) taking the shape height as a first value, and (b-4-5-2) taking the distance along the first direction between the processing region and the position obtained in the step (b-4-1) as a second value, the step (b-4-6) comprises, when the shape height is smaller than the shape depth, steps of (b-4-6-1) taking the value multiplying the shape depth by (xe2x88x921) as the first value, and (b-4-6-2) taking the distance along the first direction between the processing region and the position determined in the step (b-4-2) as the second value, the step (c-1) comprises steps of (c-1-1) obtaining, respectively about the direction I and direction J, an altitude amount candidate at either the first value in the first region or the first value in the second region, on the basis of the magnitude relation between a third value obtained by dividing the first value in the first region by the second value in the first region, and a fourth value obtained by dividing the first value in the second region by the second value in the second region, (c-1-2) taking, respectively about the direction I and direction J, either the third value or the fourth value as a slope amount candidate, on the basis of the magnitude relation between the third value and the fourth value, (c-1-3) taking the altitude amount candidate corresponding to the one with the greatest absolute value among the plural altitude amount candidates as the altitude amount, and (c-1-4) determining the film thickness increment or decrement on the basis of the altitude amount, and the absolute value of the film thickness increment or decrement is greater when the absolute value of the altitude amount is greater in the step (c-1-4), and the sign of the altitude amount and the sign of the film thickness increment or decrement are different from each other.
A fourteenth aspect of the invention relates to a method of making a mask pattern of the thirteenth aspect, wherein the step (c-1-3) comprises a step of (c-1-3-1) taking the one with the greatest absolute value among the plural slope amount candidates as the slope amount, and the film thickness increment or decrement is determined also on the basis of the slope amount in the step (c-1-4), and the absolute value of the film thickness increment or decrement is greater when the absolute value of the slope amount is greater.
A fifteenth aspect of the invention relates to a method of making a mask pattern of the thirteenth aspect, wherein the steps (b-3), (b-4), (c-1-1), and (c-1-2) are executed also in first and second directions orthogonal to each other in a stretching plane of the direction I and direction J, crossing at an equal angle with both the direction I and direction J.
A sixteenth aspect of the invention relates to a method of making a mask pattern of the first aspect, wherein the mask pattern is edited on a screen in the step (d), and a caution is visually alerted on the screen at a position where the absolute value of the correction amount exceeds a specific upper limit.
A seventeenth aspect of the invention relates to a method of making a mask pattern of the second aspect, wherein the step (c-1) includes:
(c-1-1) a resist application simulation step for simulating the mode of the resist being disposed on the object.
An eighteenth aspect of the invention relates to a method of making a mask pattern of the second aspect, wherein the step (c-2) has steps of (c-2-1) determining an equal strength plane by performing strength distribution simulation on irradiation ray for photosensitizing the resist, and (c-2-2) estimating the shape of the resist when the resist is developed, from the equal strength plane.
A nineteenth aspect of the invention relates to a method of making a mask pattern of the first aspect, wherein the actual pattern is provided by forming a resist on the object, and shaping the resist according to the mask pattern, and the step (c) includes a step of simulating the shaping.
In the invention, meanwhile, xe2x80x9cmask patternxe2x80x9d refers to the data for controlling whether or not the resist is exposed, including the data for controlling the particle rays directly drawn on the resist.
According to the mask pattern making method of the first aspect of the invention, predicting the effect of the surface shape of the object on the dimension of the actual pattern, it is fed back to the mask pattern.
Therefore, a mask pattern to obtain the actual pattern in the dimensions of the desired value can be made without actually processing the object.
According to the mask pattern making method of the second aspect of the invention, a thicker resist is formed when the degree of concavity in the processing region is stronger, and a thinner resist is formed when the degree of convexity is stronger. When the resist is thicker, the irradiation ray for changing the developing characteristic of the resist, for example, the light is absorbed more. Since the resist receives the irradiation ray from the opposite side of the processing region, the area of the resist receiving the irradiation ray passing through the mask pattern becomes smaller as going toward the processing region.
Therefore, the effectively masked region in the processing region expands, and the interval of the regions to be masked becomes narrower, so that the dimensions of the actual pattern can be predicted.
According to the mask pattern making method of the third aspect of the invention, when the first region (I0+) is in the first state (D+), and the second region (I0xe2x88x92) is in the second state (Dxe2x88x92), the surface height increases as going toward the processing region along the first direction, and the surface height decreases after passing through the processing region, so that the processing region can be judged to be convex.
To the contrary, when the first region (I0+) is in the second state (Dxe2x88x92), and the second region (I0xe2x88x92) is in the first state (D+), the surface height decreases as going toward the processing region along the first direction, and the surface height increases after passing through the processing region, so that the processing region is judged to be concave.
Therefore, the undulations in the processing region can be easily judged by simulation without trial fabrication.
According to the mask pattern making method of the fourth aspect of the invention, in the first and second regions, presence of the first or second state is judged by taking note of the maximum value and minimum value of the shape of the object.
Therefore, the undulations in the processing region are judged macroscopically, without being affected by a slight error in simulation of the shape of the object.
According to the mask pattern making method of the fifth aspect of the invention, the altitude amount is determined in consideration of both the first value of the first region and the first value of the second region.
Therefore, the altitude amount is determined depending on the degree of change of the processing shape of the first and second regions for determining the undulations, and the film thickness increment or decrement is set depending on the magnitude of the altitude amount, so that the effect of the first aspect can be easily obtained while considering the contribution of the processing shape of both first and second regions to the thickness of the resist.
According to the mask pattern making method of the sixth aspect of the invention, the slope amount is determined in consideration of both the first value of the first region and the first value of the second region.
Therefore, the film thickness increment or decrement is set depending not only on the magnitude of the altitude amount but also on the slope amount, so that the mask pattern can be correctly more precisely while considering the contribution of the processing shape of both first and second regions to the thickness of the resist.
According to the mask pattern making method of the seventh aspect of the invention, the third value refers to the degree of change, including the sign, of the shape of the object in the first region. The fourth value refers to the degree of change, including the sign, of the shape of the object in the second region.
Therefore, the altitude amount is determined depending on the degree of change of the processing shape of both first and second regions for determining undulations, and the film thickness increment or decrement is set depending on the magnitude of the altitude amount, so that the effect of the fourth aspect can be easily obtained while considering which one of the contribution of the processing shape of the first and second regions is dominant for the thickness of the resist.
According to the mask pattern making method of the eighth aspect of the invention, the slope amount refers to the degree of change, including the sign, of the shape of the object in the first and second regions.
Therefore, the film thickness increment or decrement is set not only on the magnitude of the altitude amount, but also on the slope amount, so that the mask pattern can be corrected more precisely.
According to the mask pattern making method of the ninth aspect of the invention, the irradiation ray is absorbed more when the resist is thicker, depending on the characteristic of the resist.
Therefore, by determining the pattern increment or decrement on the basis of the index, the prediction at step (c) of the first aspect can be realized.
According to the mask pattern making method of the tenth aspect of the invention, the dimensions of actual patterns are predicted respectively in two directions orthogonal to each other, so that the mask pattern can be corrected in consideration of these two directions.
Therefore, a rectangular pattern having parallel sides in two directions orthogonal to each other can be corrected easily.
According to the mask pattern making method of the eleventh aspect of the invention, undulations are judged respectively in two directions orthogonal to each other, so that the mask pattern can be corrected in consideration of these two directions.
Therefore, an more accurately mask pattern correction can be done easily.
According to the mask pattern making method of the twelfth aspect of the invention, in the first and second regions, presence of the first or second states is judged by taking note of the maximum value and minimum value of the shape of the object.
Therefore, the undulations of the processing region are judged macroscopically, without being affected by a slight error in simulation of the shape of the object.
According to the mask pattern making method of the thirteenth aspect of the invention, the third value refers to the degree of change, including the sign, of the shape of the object in the first region. The fourth value refers to the degree of change, including the sign, of the shape of the object in the second region.
Therefore, the altitude amount is determined depending on the degree of change of the processing shape of both first and second regions for determining undulations, and the film thickness increment or decrement is set depending on the magnitude of the altitude amount, so that the effect of the eleventh aspect can be easily obtained while considering which one of the contribution of the processing shape of the first and second regions is dominant for the thickness of the resist.
According to the mask pattern making method of the fourteenth aspect of the invention, the slope amount refers to the degree of change, including the sign, of the shape of the object in the first and second regions.
Therefore, the film thickness increment or decrement is set not only on the magnitude of the altitude amount, but also on the slope amount, so that the mask pattern can be corrected more precisely.
According to the mask pattern making method of the fifteenth aspect of the invention, undulations are judged in four directions mutually crossing at 45 degrees each, and step (c) is executed with the undulations relating to the direction of the greatest degree of undulations.
Therefore, the undulations are judged in more directions, so that the mask pattern can be correctly more precisely.
According to the mask pattern making method of the sixteenth aspect of the invention, the caution is visually alerted on the screen, so that the position requiring an excessive amount of correction can be easily known.
Therefore, the mask pattern can be corrected by easy operation.
According to the mask pattern making method of the seventeenth aspect of the invention, the film thickness of the resist is accurately determined in the resist application simulation step.
Therefore, the film thickness of the resist can be determined accurately, so that the dimensions of the actual pattern can be also predicted more accurately.
According to the mask pattern making method of the eighteenth aspect of the invention, the shape after development of the resist can be accurately determined in the strength distribution simulation step.
According to the mask pattern making method of the nineteenth aspect of the invention, the shape of the resist can be accurately determined in the simulation step.
Therefore, the shape of the resist can be determined accurately, and hence the dimensions of the actual pattern can be predicated more accurately.
It is therefore an object of the present invention to solve the problems and provide a technique for correcting the mask pattern without loosening the design rule or measuring all contact hole diameters.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following description of the present invention when taken in conjunction with the accompanying drawings.